This application claims priority of Korea patent Application No. 2000-24642, filed on May 9, 2000.
(a) Field of the Invention
The present invention relates to a method used in an automatic transmission for controlling shifting into neutral when the vehicle is stopped in a first speed. More particularly, the present invention relates to a method for shifting an automatic transmission into neutral when stopped in a first speed such that fuel efficiency is improved, and a load of a torque converter is reduced to minimize noise and vibrations, thereby enhancing a ride feel.
(b) Description of the Related Art
In an automatic transmission used for vehicles, a shift control system performs control to realize automatic shifting into different speeds and shift ranges according to various factors such as throttle opening, vehicle speed and load, and several engine and driving conditions detected through a plurality of sensors. That is, based on such factors, the shift control system controls a plurality of solenoid valves of a hydraulic control system such that hydraulic flow in the hydraulic control system is controlled, resulting in the shifting of the transmission into the various speeds and shift ranges.
In addition, when the driver manipulates a shift lever to a particular shift range, a manual valve of the hydraulic control system undergoes port conversion as a result of the manual valve being indexed with the shift lever. By this operation, hydraulic pressure supplied from a hydraulic pump selectively engages a plurality of friction elements of a gearshift mechanism according to the duty control of the solenoid valves, thereby realizing shifting into the desired shift range.
In such an automatic transmission, shift quality is determined by how smoothly the friction elements are engaged and disengaged. Namely, when changing shift ranges, and speeds within the ranges, the timing between the engagement of a specific set of friction elements in relation to the disengagement of another specific set of friction elements determines the shift quality of the automatic transmission. Accordingly, there have been ongoing efforts to develop improved shift control methods that enhance shift quality by better controlling the timing of the friction elements to engaged and disengaged states.
When the vehicle is stopped for a relatively short period of time (e.g., when at a red light), the driver depresses the brake pedal rather than shifting into neutral or the parking range. This forcefully stops a powertrain of the automatic transmission while in a first speed such that a rotational force of the engine is absorbed by a slip operation in a torque converter. However, by maintaining the above state in which the engine rotational force is absorbed by the slip operation in the torque converter, a substantial load is generated in the torque converter. As a result, noise and vibrations are generated so that a ride feel is reduced when stopped. Fuel consumption is also increased.
The present invention has been made in an effort to solve the above problems.
It is an object of the present invention to provide a method used in an automatic transmission for controlling shifting into neutral when the vehicle is stopped in a first speed such that fuel efficiency is improved, and so that a load of a torque converter is reduced to minimize noise and vibrations, thereby enhancing a ride feel when stopped.
To achieve the above object, the present invention provides a method used in an automatic transmission for controlling shifting into neutral when the vehicle is stopped in a first speed. The method comprises the steps of (a) determining if a vehicle speed is less than a predetermined speed; (b) determining if a grade in the road is greater than a predetermined value if the vehicle speed is less than the predetermined speed; (c) determining if a throttle valve opening is 0% if the grade of the road is greater than the predetermined value; (d) determining if a present shift speed is a first speed of a drive D range or a drive D2 range if the throttle valve opening is 0%; (e) determining if an oil temperature is greater than a predetermined temperature if the present shift speed is the first speed in the drive D range or D2 range; (f) determining if present engine rpm Ne is within a predetermined range if the oil temperature is greater than the predetermined temperature; (g) determining if output rpm of the transmission is 0 rpm if the present engine rpm is within the predetermined range; (h) determining if turbine rpm of a torque converter is 0 rpm if the output rpm of the transmission is 0 rpm; (i) determining if a brake has been depressed by the driver if the turbine rpm of the torque converter is 0 rpm; and (i) performing control into neutral if the brake has been depressed by the driver, then returning to step (c) of determining if the throttle valve opening is 0%.
If the vehicle speed is greater than the predetermined speed in step (a), a present shift state is maintained; if the grade in the road is less than the predetermined value in step (b), it is determined if the grade in the road is less than 0%, and if it is, the present shift state is maintained, and if it is not, the process is returned to step (b). Also, if any one of the conditions of steps (c) through (i) is not satisfied, N-D shifting is performed.
According to a feature of the present invention, the predetermined speed of step (a) is 30 km/h.
According to another feature of the present invention, the predetermined value of step (b) is 3.5%.
According to yet another feature of the present invention, the predetermined temperature of step (e) is 20xc2x0 C.
According to still yet another feature of the present invention, the predetermined range of step (f) is between 350 rpm and 1000 rpm.
According to still yet another feature of the present invention, after control into neutral of step (j) is performed, it is determined if a difference in the turbine rpm and the output rpm is greater than 100 rpm, and if the difference in rpm is greater than 100 rpm, an ECU controls an air intake controller and an ignition timing controller such that idle control in the neutral range is performed, and if the difference in rpm less than or equal to 100 rpm, the ECU controls the air intake controller and the ignition timing controller such that idle control in the drive D range is performed.
According to still yet another feature of the present invention, the predetermined rpm is 100 rpm.